Preparation Of Zirconium-based Solid Base And Its Catalytic Synthesis Of Glycerol Carbonate

The multifunctional structure of glycerol carbonate（GC）makes it a chemical intermediate with high added value,and it is widely used in medicine,coating,food,cosmetics and other industries.especially in the context of the massive overcapacity of glycerol in the booming biodiesel production process,the use of glycerol as a raw material to synthesize GC by transesterification has realized the conversion and utilization of glycerol with high added value,which is favored by the majority of researchers.In the process of transesterification to synthesize GC,the most important thing is to choose an efficient catalyst.Commonly used catalysts for this transesterification are homogeneous base catalysts and heterogeneous base catalysts.The advantage of homogeneous base catalysts is that they have higher However,there are common problems such as difficult separation of reaction products and cumbersome post-processing,so heterogeneous base catalysts are mostly used to catalyze glycerol transesterification to synthesize GC,but its low catalytic activity and poor stability are the key problems that have not been solved.This thesis aims to explore the preparation of zirconium-based solid base catalysts with high activity,high stability and easy product separation.The catalysts are characterized and analyzed by means of XRD,BET,CO₂-TPD,SEM,ICP-OES,XPS,etc.,and the catalysts are studied.Effects of the structure and reaction conditions on the synthesis of GC by transesterification of glycerol with dimethyl carbonate（DMC）.The main research contents and results are as follows:（1）Three kinds of modified zirconium-based solid base catalysts were prepared by alkali reflux method,which were used in the transesterification reaction of glycerol and DMC,and the best catalyst ZrO₂-KOH was screened out,and the structure and transesterification process of the catalyst were investigated.Influence of conditional parameters on catalytic performance.The conversion rate of glycerol was 99.43%under the optimal process conditions;the conversion rate of glycerol dropped to 66.12%after five repeated uses,and it was confirmed that the reason for the significant decrease was the active component K impregnated on the surface of the catalyst.The key to the formation of strong basic sites is the strong interaction of the remaining K⁺into the ZrO₂ structure,It is the formation of such strongly basic sites that exhibit excellent catalytic activity.（2）In view of the problem of loss of active components and poor stability in the previous part,three kinds of alkali metal zirconium-based solid base catalysts were prepared by in-situ introduction of alkali metal by citric acid complex method.The high specific surface area achieved the best conversion of glycerol of 54.5%.It is shown that the specific surface area,basicity and total alkali content of the catalyst are the key factors affecting the catalytic activity of the catalyst.When using Na₂ZrO₃ catalyst,the amount of catalyst is3 wt%,the material ratio of glycerol to DMC is 1:3,and the reaction is carried out at 70℃for 1.5 h,and the conversion rate of glycerol obtained can reach 99.36%.The conversion rate of glycerol was 76.92%after five cycles of use,maintaining good stability.The activation energy of the reaction was calculated to be 43.95KJ/mol in the kinetic study of the transesterification reaction,The lower the activation energy of the reaction,the higher the catalytic activity of the catalyst.（3）The zirconium-based solid base catalyst was prepared by in-situ introduction of alkaline earth metal by citric acid complexation.The CaZrO₃ catalyst had the best catalytic activity and was screened as the best catalyst.Under the condition that the dosage of CaZrO₃ catalyst is 2 wt%,the material ratio of glycerol to DMC is 1:2,the reaction temperature is 90℃,and the reaction time is 2 h,the best conversion rate of glycerol is 98.03%.The conversion rate of glycerol can still reach 86.81%after five repeated use,showing excellent catalytic stability.The activation energy of the catalyst for glycerol transesterification was 49.66 KJ/mol.